The invention relates to a process and device for producing a series of adjacent grooves with mutually equal pitch by the broaching of the grooves in the peripheral surface of a body of rotation.
According to known processes, grooves are made in such a way that only one broaching tool works on a groove of the workpiece, said grooves thus being worked individually and in succession, whereby the workpiece, after a groove is broached, is turned further by a pitch t. Because of the generally low broaching speeds which, especially with materials that are highly heat resistant, can be as low as 2 m/min, in this broaching process, a substantially long manufacturing time results which correspondingly raises the cost of production.
Another drawback in the known method is that there is insufficient adaptability of an available machine capacity to what is actually needed. If deep, comparatively complicated grooves are broached, it is necessary to have correspondingly large broaching machines, with long tool strokes and great cutting forces. If, on the other hand, only small grooves with a simple profile and comparatively little material removal are to be broached, they have to be correspondingly small broaching machines which execute a short tool stroke and utilize low cutting forces. However, since the machine set-up has to be designed for the maximum required power, these machines then frequently work in an uneconomical partial load range.
Lastly, it has been necessary thus far, in the case of particular grooves, when the broaching tool is longer than the tool carrier of the broaching machine, to divide the total working of the groove into manufacturing segments, the operating being effected in such a way that with a first part piece of the broaching tool there is a preliminary broaching of the groove, and thereafter this first part piece is exchanged for a second part piece of the broaching tool, with which the preliminary broached groove is finished in a second passage. This process quite particularly requires long manufacturing times and attempts have been made to meet the problems that arise in consideration of the long manufacturing times and in consideration of the poor adaptation possibilities in the available machine capacity, in the case of workpieces with grooves coaxial to the axis of the workpiece, by clamping two workpieces one above the other to reduce projection time. However, because of the greater penetration depth of the two workpieces, the broaching tool chambers for removing material have to be larger, whereby the length of the tool is increased, and again the machining time. For this reason, the present invention has as an object to find a broaching process with which the unacceptably long manufacturing times can be avoided, allowing better utilization of the available machine capacity, no matter whether there are to be deep complex grooves, or those where there is little removal of material.
This problem is solved according to an aspect of the present invention by a process that is characterized by simultaneously broaching two adjacent grooves in one broaching stroke by means of two broaching tools which are clamped at the distance and in the angular position of the pitch of the groove that is to be produced.
An important advantage created by this method according to the present invention resides in the shortening of the machining time, that two grooves can be worked at once. Thus, depending upon the type of profile or step, either there can be final working of two respective grooves in one broaching stroke, or one broaching tool can be a preliminary broaching tool and the other a final broaching tool such that with one broaching stroke, one groove will be preliminarily broached and simultaneously an adjacent one will be finished, whereby only before the first broaching stroke is executed with the two tools is there a first initial groove made in the workpiece.
Another important advantage of the simultaneous broaching of two adjacent grooves according to the present invention consists in that available machine capacity can be better adapted to the actual broaching operation. In this way, only a relatively short work stroke is needed for deep, complicated grooves since the total length of the broaching tool is divided into two partial lengths, leading to the end result that smaller broaching machines can be utilized for such complicated grooves.
A preferred embodiment of the process according to the present invention comprises the following successive steps:
(a) By means of a single clamped preliminary broaching tool, an initial groove is produced in a first broaching stroke, with the desired preliminary broaching profile;
(b) A final broaching tool is clamped next to the preliminary broaching tool at a distance and in the angular position of the pitch of the groove that is to be produced;
(c) The workpiece is adjusted in such a way that the initial groove will correspond to the final broaching tool in height and position of the finished groove;
(d) In a second broaching stroke, simultaneously, with use of both broaching tools, the initial groove is finished, and a second groove is preliminarily broached; and
(e) By further turning of the workpiece, for execution of another broaching stroke with the two tools simultaneously, all further grooves of the workpiece are produced.
By working the initial groove in a first broaching stoke with only one broaching tool, the workpiece does not need to be reclamped, but can be finished in a single clamping.
Moreover, the invention relates to a broaching process as described above, in which the direction of the grooves to be produced is not parallel to the direction of the axis of the body of rotation (workpiece) and is characterized in that the initial section of the final broaching tool is made as a compensating tool with which errors of angle present in the preliminarily broached groove can be evened out. Since both the preliminary broaching tool and likewise the final broaching tool are fixed on the same carriage, only the direction of movement of the final broaching tool can coincide with the axial direction of the groove that is to be produced, whereas the direction of movement of the preliminary broaching tool, in this case, describes a small angle with the axial direction of the groove to be preliminarily broached. The machining errors caused by this can be easily compensated for by the compensating tool portion of the final broaching tool without producing excessive stress on a section of the final broaching tool from it having to cut to an excessive depth of the workpiece. Neither will an inadequate offset remain on the groove, to prevent attainment of the correct final configuration.
The process is specially advantageous in production of retaining grooves for blades on the rotor of a turbine, since here a plurality of grooves must be broached in a material that is difficult to machine in a metal-removing process with low cutting speeds.
In addition to the above-noted process, the invention relates to a device for execution of the above-described process and is characterized, according to a preferred embodiment in that a T-shaped supporting strip is adapted to the broaching tools and the opposed arrangement of the grooves and is fastened on a tool carriage via a broaching girder. The T-shaped support is formed with two angle chambers within a respective one of which the preliminary and final broaching tools are clamped, whereby filler pieces with the metal removal profile of the broaching tool are set in at those places where there is a broaching tool section only on one side of the supporting strip. Because of the T-shaped supporting strip, it is possible to have a very small distance between the two adjacent broaching tools, which is very important when the pitch of the groove to be broached is very narrow. Another advantage of this type of clamping consists in that with conventional broaching machines, the usual tool holders require only slight modification, namely the setting in of the T-shaped support strip, so that operations can be effected with a universal machine. Finally, because of the opposed clamping of the two broaching tools, there is very rigid clamping of the individual tools, since the adjacent tools and its clamping elements can serve as a brace.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration, a single embodiment in accordance with the present invention .